ERADICATE poison oak!
What will KILL poison oak? I've been using Crossbow for decades with only marginal success. Even applying every year only seems to stunt it. An acquaintance in the Ag chemicals field told me to try ALY, but while it turned himalayan blackberries into skeletons, the poison oak re-grew even more robustly from the same plants the next season. My location south of Sherwood appears to be ideally suited to the plant. Madrone trees also thrive here, very similar to the region from Grants Pass south to the California border.
Clackamas County Oregon
Consider using the Streamline or Garlon products/directions as indicated in the PNW handbook at the link below. Aminocyclopylachlor has very good activity on a number of brush/woody species and is probably a little better than metsulfuron (Ally) or triclopyr (Garlon and Crossbow). Be careful not to drift onto desirable trees however.